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ABSTRAK Monika Putri Maharani
PUBLIC Suharsiyah

Indonesia has a target of reducing 29% GHG emissions by 2030 (NDC, 2022) reaching net-zero emissions in 2060 (LTS-LCCR, 2021) and obtain 1 million BOPD oil production and 12 BSCFD gas production in 2030. Oil and gas companies have particular challenges to achieve the target in line with paying attention to national energy security despite the oil reserve and production declining since 1995 because of the maturity of the fields. The increasing global concern over greenhouse gas emissions and the need for increase the production has led to the exploration of various technologies. Carbon capture and storage (CCS) is recognized as a promising approach to reduce CO2 emissions, while enhanced oil recovery (EOR) methods offer the potential for increased oil production. Other than CO2, methene is one of the main sources of emissions from the natural gas production lost. As a result of further studies, combining methane align with CO2 as applying Water Alternating Gas (WAG) injection could increase the recovery in line with CO2 sequestration. In this study, CMG GEMTM simulator is used to modelling Water Alternating Gas CO2-CH4 and identify the effect of operational parameter to propose the most optimum scenario to be applied in ‘B” Structure and “S” Field reservoir. The simulation and forecast production were done for 16 years starting from January 2021 and observe the storage capacity until 30 years after last injection stopped. The sensitivity studies were conducted to identify the effect of operational parameter and optimum scenario to gain promising oil recovery and storage capacity. Gas slug size and cycle were varied to find the most optimum parameters. This study also observing the CO2 sequestration for 30 years, to evaluate the potential for CO2 leakage from storage sites to the surface through caprocks, it is necessary to examine both the current sealing capability of the rock and its susceptibility to change when exposed to CO2. The aim of this paper is present a comprehensive overview about the influence of WAG CH2-CO4 to sealing integrity of the caprock in "B" Structure of the "S" Field. The result of this study shows the higher recovery factor was achieved when the percentage of the gas slug size and number of cycle decrease. Furthermore, the storage capacity is increase when increasing gas slug size and number of cycles. To find the most optimum scenario, this study uses co-optimization function to combine the oil recovery and CO2 storage. In addition to storage capacity, preservation of caprock sealing study shows that the presence of CH4 can minimize the occurrence of leakage. This suggests that the caprock acts as an effective barrier, preventing the migration and escape of CO2 from the reservoir, thus enhancing the overall storage integrity, and minimizing potential leakage pathways. Implementing Water Alternating Gas CO2-CH4 could improve the recovery factor up to 56.26% and cut environmental footprint until 62.1 Kton of net CO2 and 13.5 Kton of net CH4 to be stored in reservoir. As the result, utilization of WAG CH4-CO2 injection in the "B" Structure of the "S" Field reservoir offers substantial advantages and represents a pioneering technology with promising implications.